1. Field of the Invention
The present invention relates to a method of controlling a shock energy absorption system to minimize instantaneous payload acceleration. More particularly, the invention is a system and method for determining and applying with an energy absorption system the required constant oppositional force to achieve optimal energy dissipation over the full or partial stroke of an absorber so as to minimize the instantaneous load on the payload.
2. Description of the Background
The minimization of shock load-induced injury is a critical issue in seat suspension design. Scat occupants can suffer spinal, pelvic and other injuries as a result of harsh vertical/crash landings of aircraft, a problem to which rotorcraft are particularly susceptible. Extreme vertical shock loads are also experienced by land and marine vehicles during high speed operations and in harsh environmental conditions. The presence of vertical impact force attenuation systems in vehicle crashes is one of the primary factors in determining occupant survivability. Further, the risk and severity of an injury to vehicle occupants can be considerably reduced if the vehicle is equipped with crashworthy seat designs including seat suspension systems that can mitigate the vertical shock loads. In addition, such shock absorber system can isolate occupants from harmful operational vibrations, mitigate severe and repetitive operational impact shocks, and protect vital devices and electronics.
Conventional passive shock mitigation approaches are limited by their inability to adapt to varying shock levels or payload (occupant) weights. More specifically, passive suspension systems may be tuned for a maximum expected shock amplitude and/or the heaviest expected occupant weight but would provide far from optimal results for smaller payloads and/or in lower amplitude shock conditions. In such a case, the load transmitted to the payload via the shock absorber would be unnecessarily high (causing an unnecessary risk of injury) and the full dissipative capability of the entire absorber stroke would not be used. Alternatively, if the passive suspension system were tuned for lower amplitude shock and/or a lower payload (occupant) weight, the suspension would be too “soft” for a heavier payload or higher amplitude shock condition, more often resulting in the absorber meeting is stroke end-stop (i.e. bottoming out), again causing an unnecessary risk of injury.
There has thus been significant interest in both the private and public (military) sectors in developing an adaptive energy absorption system that will automatically adjust its energy absorbing characteristics to payload (occupant) weight and real-time environmental measurements. U.S. patent application Ser. Nos. 11/670,773 and 11/670,761 (both titled Adaptive Energy Absorption System for Vehicle Seat filed Feb. 2, 2007) by the present applicant are two such systems, each of which is incorporated herein by reference. An effective method of controlling such adaptive energy absorption system is needed in order to achieve the shock mitigation goal. Additional relevant patents include U.S. Pat. No. 6,732,033 (2004) to LaPlante et al., U.S. Pat. No. 6,311,110 (2001) to Ivers et al. U.S. Pat. No. 6,112,866 (2000) to Boichot et al. and U.S. Pat. No. 5,276,622 (1994) to Miller et al.